1. Field of the Invention
The present invention is related to devices enabling shifting of gears for bicycles of the type having a chain and pinion transmission.
2. Discussion of Background Material
In currently known bicycles, gear shifting is done by means of a device ensuring the displacement of the chain in engagement with a gear, towards another gear of a different diameter, thus ensuring a modification of the transmission ratio. We are aware of devices of this type, also called gear shift devices, and which comprise an upper body fixed to the frame of the bicycle, and a lower body retaining the chain, which is movably connected with respect to the upper body by a parallelogram-shaped structure capable of oscillating transversely in order to laterally displace the chain and enable the various gear shifts. The parallelogram-shaped structure is constituted by a fairly complex assembly having a plurality of rotational connection rods. The movements of the parallelogram are controlled by the action of a flexible metallic cable, whose end is connected to a lever fixed on the frame in a rotational manner, which the cyclist must maneuver in order to thus carry out the various shifts of gears. Such devices have been described for example, in the French Patent Applications Nos. 2,620,104, 2,637,249 and 2,639,313.
These devices, although they have been improved, are not entirely satisfactory and have a certain number of disadvantages. Indeed, the gear shift devices that are currently on the market, as we are aware, have high manufacturing costs and are not totally reliable in use. In addition, they are relatively heavy and are not completely precise as regards the position of the chain in engagement. To solve the problem linked to the lack of precision in positioning, some manufacturers have provided an indexing system of the control lever. But in light of transmission by metallic cable, it is completely impractical to want to impose a well defined position to the mobile element of the gear shift, and it is generally the cyclist who intuitively places the control lever in the most appropriate position, and then refines the adjustment by using the noise that the chain makes when it is not quite in the correct position. As such, it is easy to understand that the cyclist is more preoccupied by shifting gears than by pedaling. Also, the cyclist must, in most cases, leave his handle bar to move the gear shifting lever, which, under the best of circumstances, can hardly be considered ideal, especially for competitive cyclists who ought only to have to concentrate on their pedaling and steering.
The present invention aims to solve these various disadvantages of prior art gear shift devices and suggests a new idea for a gear shift that provides greater indexing precision, ease of use, possibility of multiplying the controls by placing them at different areas and especially on the handle bar, better reliability, and less weight and cost. The device according to the invention also enables gear shifting with a minimum control energy.